1 /*
2 * Copyright (c) 2013, 2021, Red Hat, Inc. All rights reserved.
3 * Copyright (C) 2022 THL A29 Limited, a Tencent company. All rights reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "precompiled.hpp"
27 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
28 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
29 #include "gc/shenandoah/shenandoahControlThread.hpp"
30 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
31 #include "gc/shenandoah/shenandoahFreeSet.hpp"
32 #include "gc/shenandoah/shenandoahFullGC.hpp"
33 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
35 #include "gc/shenandoah/shenandoahMark.inline.hpp"
36 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
37 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
38 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
39 #include "gc/shenandoah/shenandoahUtils.hpp"
40 #include "gc/shenandoah/shenandoahVMOperations.hpp"
41 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
42 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
43 #include "memory/iterator.hpp"
44 #include "memory/metaspaceUtils.hpp"
45 #include "memory/metaspaceStats.hpp"
46 #include "memory/universe.hpp"
47 #include "runtime/atomic.hpp"
48
49 ShenandoahControlThread::ShenandoahControlThread() :
50 ConcurrentGCThread(),
51 _alloc_failure_waiters_lock(Mutex::safepoint-2, "ShenandoahAllocFailureGC_lock", true),
52 _gc_waiters_lock(Mutex::safepoint-2, "ShenandoahRequestedGC_lock", true),
53 _periodic_task(this),
54 _requested_gc_cause(GCCause::_no_cause_specified),
55 _degen_point(ShenandoahGC::_degenerated_outside_cycle),
56 _allocs_seen(0) {
57 set_name("Shenandoah Control Thread");
58 reset_gc_id();
59 create_and_start();
60 _periodic_task.enroll();
61 if (ShenandoahPacing) {
62 _periodic_pacer_notify_task.enroll();
63 }
64 }
65
66 ShenandoahControlThread::~ShenandoahControlThread() {
67 // This is here so that super is called.
68 }
69
70 void ShenandoahPeriodicTask::task() {
71 _thread->handle_force_counters_update();
72 _thread->handle_counters_update();
73 }
74
75 void ShenandoahPeriodicPacerNotify::task() {
76 assert(ShenandoahPacing, "Should not be here otherwise");
77 ShenandoahHeap::heap()->pacer()->notify_waiters();
78 }
79
80 void ShenandoahControlThread::run_service() {
81 ShenandoahHeap* heap = ShenandoahHeap::heap();
82
83 GCMode default_mode = concurrent_normal;
84 GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
85 int sleep = ShenandoahControlIntervalMin;
86
87 double last_shrink_time = os::elapsedTime();
88 double last_sleep_adjust_time = os::elapsedTime();
89
90 // Shrink period avoids constantly polling regions for shrinking.
91 // Having a period 10x lower than the delay would mean we hit the
92 // shrinking with lag of less than 1/10-th of true delay.
93 // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
94 double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
95
96 ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
97 ShenandoahHeuristics* heuristics = heap->heuristics();
98 while (!in_graceful_shutdown() && !should_terminate()) {
99 // Figure out if we have pending requests.
100 bool alloc_failure_pending = _alloc_failure_gc.is_set();
101 bool is_gc_requested = _gc_requested.is_set();
102 GCCause::Cause requested_gc_cause = _requested_gc_cause;
103 bool explicit_gc_requested = is_gc_requested && is_explicit_gc(requested_gc_cause);
104 bool implicit_gc_requested = is_gc_requested && !is_explicit_gc(requested_gc_cause);
105
106 // This control loop iteration have seen this much allocations.
107 size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0, memory_order_relaxed);
108
109 // Check if we have seen a new target for soft max heap size.
110 bool soft_max_changed = check_soft_max_changed();
111
112 // Choose which GC mode to run in. The block below should select a single mode.
113 GCMode mode = none;
114 GCCause::Cause cause = GCCause::_last_gc_cause;
115 ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
116
117 if (alloc_failure_pending) {
118 // Allocation failure takes precedence: we have to deal with it first thing
119 log_info(gc)("Trigger: Handle Allocation Failure");
120
121 cause = GCCause::_allocation_failure;
122
123 // Consume the degen point, and seed it with default value
124 degen_point = _degen_point;
125 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
126
127 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle()) {
128 heuristics->record_allocation_failure_gc();
129 policy->record_alloc_failure_to_degenerated(degen_point);
130 mode = stw_degenerated;
131 } else {
132 heuristics->record_allocation_failure_gc();
133 policy->record_alloc_failure_to_full();
134 mode = stw_full;
135 }
136
137 } else if (explicit_gc_requested) {
138 cause = requested_gc_cause;
139 log_info(gc)("Trigger: Explicit GC request (%s)", GCCause::to_string(cause));
140
141 heuristics->record_requested_gc();
142
143 if (ExplicitGCInvokesConcurrent) {
144 policy->record_explicit_to_concurrent();
145 mode = default_mode;
146 // Unload and clean up everything
147 heap->set_unload_classes(heuristics->can_unload_classes());
148 } else {
149 policy->record_explicit_to_full();
150 mode = stw_full;
151 }
152 } else if (implicit_gc_requested) {
153 cause = requested_gc_cause;
154 log_info(gc)("Trigger: Implicit GC request (%s)", GCCause::to_string(cause));
155
156 heuristics->record_requested_gc();
157
158 if (ShenandoahImplicitGCInvokesConcurrent) {
159 policy->record_implicit_to_concurrent();
160 mode = default_mode;
161
162 // Unload and clean up everything
163 heap->set_unload_classes(heuristics->can_unload_classes());
164 } else {
165 policy->record_implicit_to_full();
166 mode = stw_full;
167 }
168 } else {
169 // Potential normal cycle: ask heuristics if it wants to act
170 if (heuristics->should_start_gc()) {
171 mode = default_mode;
172 cause = default_cause;
173 }
174
175 // Ask policy if this cycle wants to process references or unload classes
176 heap->set_unload_classes(heuristics->should_unload_classes());
177 }
178
179 // Blow all soft references on this cycle, if handling allocation failure,
180 // either implicit or explicit GC request, or we are requested to do so unconditionally.
181 if (alloc_failure_pending || implicit_gc_requested || explicit_gc_requested || ShenandoahAlwaysClearSoftRefs) {
182 heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
183 }
184
185 bool gc_requested = (mode != none);
186 assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
187
188 if (gc_requested) {
189 // GC is starting, bump the internal ID
190 update_gc_id();
191
192 heap->reset_bytes_allocated_since_gc_start();
193
194 MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
195
196 // If GC was requested, we are sampling the counters even without actual triggers
197 // from allocation machinery. This captures GC phases more accurately.
198 set_forced_counters_update(true);
199
200 // If GC was requested, we better dump freeset data for performance debugging
201 {
202 ShenandoahHeapLocker locker(heap->lock());
203 heap->free_set()->log_status();
204 }
205
206 switch (mode) {
207 case concurrent_normal:
208 service_concurrent_normal_cycle(cause);
209 break;
210 case stw_degenerated:
211 service_stw_degenerated_cycle(cause, degen_point);
212 break;
213 case stw_full:
214 service_stw_full_cycle(cause);
215 break;
216 default:
217 ShouldNotReachHere();
218 }
219
220 // If this was the requested GC cycle, notify waiters about it
221 if (explicit_gc_requested || implicit_gc_requested) {
222 notify_gc_waiters();
223 }
224
225 // If this was the allocation failure GC cycle, notify waiters about it
226 if (alloc_failure_pending) {
227 notify_alloc_failure_waiters();
228 }
229
230 // Report current free set state at the end of cycle, whether
231 // it is a normal completion, or the abort.
232 {
233 ShenandoahHeapLocker locker(heap->lock());
234 heap->free_set()->log_status();
235
236 // Notify Universe about new heap usage. This has implications for
237 // global soft refs policy, and we better report it every time heap
238 // usage goes down.
239 Universe::heap()->update_capacity_and_used_at_gc();
240
241 // Signal that we have completed a visit to all live objects.
242 Universe::heap()->record_whole_heap_examined_timestamp();
243 }
244
245 // Disable forced counters update, and update counters one more time
246 // to capture the state at the end of GC session.
247 handle_force_counters_update();
248 set_forced_counters_update(false);
249
250 // Retract forceful part of soft refs policy
251 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
252
253 // Clear metaspace oom flag, if current cycle unloaded classes
254 if (heap->unload_classes()) {
255 heuristics->clear_metaspace_oom();
256 }
257
258 // Commit worker statistics to cycle data
259 heap->phase_timings()->flush_par_workers_to_cycle();
260 if (ShenandoahPacing) {
261 heap->pacer()->flush_stats_to_cycle();
262 }
263
264 // Print GC stats for current cycle
265 {
266 LogTarget(Info, gc, stats) lt;
267 if (lt.is_enabled()) {
268 ResourceMark rm;
269 LogStream ls(lt);
270 heap->phase_timings()->print_cycle_on(&ls);
271 if (ShenandoahPacing) {
272 heap->pacer()->print_cycle_on(&ls);
273 }
274 }
275 }
276
277 // Commit statistics to globals
278 heap->phase_timings()->flush_cycle_to_global();
279
280 // Print Metaspace change following GC (if logging is enabled).
281 MetaspaceUtils::print_metaspace_change(meta_sizes);
282
283 // GC is over, we are at idle now
284 if (ShenandoahPacing) {
285 heap->pacer()->setup_for_idle();
286 }
287 } else {
288 // Allow allocators to know we have seen this much regions
289 if (ShenandoahPacing && (allocs_seen > 0)) {
290 heap->pacer()->report_alloc(allocs_seen);
291 }
292 }
293
294 double current = os::elapsedTime();
295
296 if (ShenandoahUncommit && (explicit_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
297 // Explicit GC tries to uncommit everything down to min capacity.
298 // Soft max change tries to uncommit everything down to target capacity.
299 // Periodic uncommit tries to uncommit suitable regions down to min capacity.
300
301 double shrink_before = (explicit_gc_requested || soft_max_changed) ?
302 current :
303 current - (ShenandoahUncommitDelay / 1000.0);
304
305 size_t shrink_until = soft_max_changed ?
306 heap->soft_max_capacity() :
307 heap->min_capacity();
308
309 service_uncommit(shrink_before, shrink_until);
310 heap->phase_timings()->flush_cycle_to_global();
311 last_shrink_time = current;
312 }
313
314 // Wait before performing the next action. If allocation happened during this wait,
315 // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
316 // back off exponentially.
317 if (_heap_changed.try_unset()) {
318 sleep = ShenandoahControlIntervalMin;
319 } else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
320 sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
321 last_sleep_adjust_time = current;
322 }
323 os::naked_short_sleep(sleep);
324 }
325
326 // Wait for the actual stop(), can't leave run_service() earlier.
327 while (!should_terminate()) {
328 os::naked_short_sleep(ShenandoahControlIntervalMin);
329 }
330 }
331
332 bool ShenandoahControlThread::check_soft_max_changed() const {
333 ShenandoahHeap* heap = ShenandoahHeap::heap();
334 size_t new_soft_max = Atomic::load(&SoftMaxHeapSize);
335 size_t old_soft_max = heap->soft_max_capacity();
336 if (new_soft_max != old_soft_max) {
337 new_soft_max = MAX2(heap->min_capacity(), new_soft_max);
338 new_soft_max = MIN2(heap->max_capacity(), new_soft_max);
339 if (new_soft_max != old_soft_max) {
340 log_info(gc)("Soft Max Heap Size: " SIZE_FORMAT "%s -> " SIZE_FORMAT "%s",
341 byte_size_in_proper_unit(old_soft_max), proper_unit_for_byte_size(old_soft_max),
342 byte_size_in_proper_unit(new_soft_max), proper_unit_for_byte_size(new_soft_max)
343 );
344 heap->set_soft_max_capacity(new_soft_max);
345 return true;
346 }
347 }
348 return false;
349 }
350
351 void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
352 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
353 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
354 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
355 // tries to evac something and no memory is available), cycle degrades to Full GC.
356 //
357 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
358 // heuristics says there are no regions to compact, and all the collection comes from immediately
359 // reclaimable regions.
360 //
361 // ................................................................................................
362 //
363 // (immediate garbage shortcut) Concurrent GC
364 // /-------------------------------------------\
365 // | |
366 // | |
367 // | |
368 // | v
369 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
370 // | | | ^
371 // | (af) | (af) | (af) |
372 // ..................|....................|.................|..............|.......................
373 // | | | |
374 // | | | | Degenerated GC
375 // v v v |
376 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
377 // | | | ^
378 // | (af) | (af) | (af) |
379 // ..................|....................|.................|..............|.......................
380 // | | | |
381 // | v | | Full GC
382 // \------------------->o<----------------/ |
383 // | |
384 // v |
385 // Full GC --------------------------/
386 //
387 ShenandoahHeap* heap = ShenandoahHeap::heap();
388 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
389
390 GCIdMark gc_id_mark;
391 ShenandoahGCSession session(cause);
392
393 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
394
395 ShenandoahConcurrentGC gc;
396 if (gc.collect(cause)) {
397 // Cycle is complete
398 heap->heuristics()->record_success_concurrent();
399 heap->shenandoah_policy()->record_success_concurrent();
400 } else {
401 assert(heap->cancelled_gc(), "Must have been cancelled");
402 check_cancellation_or_degen(gc.degen_point());
403 }
404 }
405
406 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
407 ShenandoahHeap* heap = ShenandoahHeap::heap();
408 if (heap->cancelled_gc()) {
409 assert (is_alloc_failure_gc() || in_graceful_shutdown(), "Cancel GC either for alloc failure GC, or gracefully exiting");
410 if (!in_graceful_shutdown()) {
411 assert (_degen_point == ShenandoahGC::_degenerated_outside_cycle,
412 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
413 _degen_point = point;
414 }
415 return true;
416 }
417 return false;
418 }
419
420 void ShenandoahControlThread::stop_service() {
421 // Nothing to do here.
422 }
423
424 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
425 GCIdMark gc_id_mark;
426 ShenandoahGCSession session(cause);
427
428 ShenandoahFullGC gc;
429 gc.collect(cause);
430
431 ShenandoahHeap* const heap = ShenandoahHeap::heap();
432 heap->heuristics()->record_success_full();
433 heap->shenandoah_policy()->record_success_full();
434 }
435
436 void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
437 assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
438
439 GCIdMark gc_id_mark;
440 ShenandoahGCSession session(cause);
441
442 ShenandoahDegenGC gc(point);
443 gc.collect(cause);
444
445 ShenandoahHeap* const heap = ShenandoahHeap::heap();
446 heap->heuristics()->record_success_degenerated();
447 heap->shenandoah_policy()->record_success_degenerated();
448 }
449
450 void ShenandoahControlThread::service_uncommit(double shrink_before, size_t shrink_until) {
451 ShenandoahHeap* heap = ShenandoahHeap::heap();
452
453 // Determine if there is work to do. This avoids taking heap lock if there is
454 // no work available, avoids spamming logs with superfluous logging messages,
455 // and minimises the amount of work while locks are taken.
456
457 if (heap->committed() <= shrink_until) return;
458
459 bool has_work = false;
460 for (size_t i = 0; i < heap->num_regions(); i++) {
461 ShenandoahHeapRegion *r = heap->get_region(i);
462 if (r->is_empty_committed() && (r->empty_time() < shrink_before)) {
463 has_work = true;
464 break;
465 }
466 }
467
468 if (has_work) {
469 heap->entry_uncommit(shrink_before, shrink_until);
470 }
471 }
472
473 bool ShenandoahControlThread::is_explicit_gc(GCCause::Cause cause) const {
474 return GCCause::is_user_requested_gc(cause) ||
475 GCCause::is_serviceability_requested_gc(cause);
476 }
477
478 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
479 assert(GCCause::is_user_requested_gc(cause) ||
480 GCCause::is_serviceability_requested_gc(cause) ||
481 cause == GCCause::_metadata_GC_clear_soft_refs ||
482 cause == GCCause::_codecache_GC_aggressive ||
483 cause == GCCause::_codecache_GC_threshold ||
484 cause == GCCause::_full_gc_alot ||
485 cause == GCCause::_wb_young_gc ||
486 cause == GCCause::_wb_full_gc ||
487 cause == GCCause::_wb_breakpoint ||
488 cause == GCCause::_scavenge_alot,
489 "only requested GCs here: %s", GCCause::to_string(cause));
490
491 if (is_explicit_gc(cause)) {
492 if (!DisableExplicitGC) {
493 handle_requested_gc(cause);
494 }
495 } else {
496 handle_requested_gc(cause);
497 }
498 }
499
500 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
501 // Make sure we have at least one complete GC cycle before unblocking
502 // from the explicit GC request.
503 //
504 // This is especially important for weak references cleanup and/or native
505 // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
506 // comes very late in the already running cycle, it would miss lots of new
507 // opportunities for cleanup that were made available before the caller
508 // requested the GC.
509
510 MonitorLocker ml(&_gc_waiters_lock);
511 size_t current_gc_id = get_gc_id();
512 size_t required_gc_id = current_gc_id + 1;
513 while (current_gc_id < required_gc_id) {
514 // Although setting gc request is under _gc_waiters_lock, but read side (run_service())
515 // does not take the lock. We need to enforce following order, so that read side sees
516 // latest requested gc cause when the flag is set.
517 _requested_gc_cause = cause;
518 _gc_requested.set();
519
520 if (cause != GCCause::_wb_breakpoint) {
521 ml.wait();
522 }
523 current_gc_id = get_gc_id();
524 }
525 }
526
527 void ShenandoahControlThread::handle_alloc_failure(ShenandoahAllocRequest& req) {
528 ShenandoahHeap* heap = ShenandoahHeap::heap();
529
530 assert(current()->is_Java_thread(), "expect Java thread here");
531
532 if (try_set_alloc_failure_gc()) {
533 // Only report the first allocation failure
534 log_info(gc)("Failed to allocate %s, " SIZE_FORMAT "%s",
535 req.type_string(),
536 byte_size_in_proper_unit(req.size() * HeapWordSize), proper_unit_for_byte_size(req.size() * HeapWordSize));
537
538 // Now that alloc failure GC is scheduled, we can abort everything else
539 heap->cancel_gc(GCCause::_allocation_failure);
540 }
541
542 MonitorLocker ml(&_alloc_failure_waiters_lock);
543 while (is_alloc_failure_gc()) {
544 ml.wait();
545 }
546 }
547
548 void ShenandoahControlThread::handle_alloc_failure_evac(size_t words) {
549 ShenandoahHeap* heap = ShenandoahHeap::heap();
550
551 if (try_set_alloc_failure_gc()) {
552 // Only report the first allocation failure
553 log_info(gc)("Failed to allocate " SIZE_FORMAT "%s for evacuation",
554 byte_size_in_proper_unit(words * HeapWordSize), proper_unit_for_byte_size(words * HeapWordSize));
555 }
556
557 // Forcefully report allocation failure
583 _do_counters_update.unset();
584 ShenandoahHeap::heap()->monitoring_support()->update_counters();
585 }
586 }
587
588 void ShenandoahControlThread::handle_force_counters_update() {
589 if (_force_counters_update.is_set()) {
590 _do_counters_update.unset(); // reset these too, we do update now!
591 ShenandoahHeap::heap()->monitoring_support()->update_counters();
592 }
593 }
594
595 void ShenandoahControlThread::notify_heap_changed() {
596 // This is called from allocation path, and thus should be fast.
597
598 // Update monitoring counters when we took a new region. This amortizes the
599 // update costs on slow path.
600 if (_do_counters_update.is_unset()) {
601 _do_counters_update.set();
602 }
603 // Notify that something had changed.
604 if (_heap_changed.is_unset()) {
605 _heap_changed.set();
606 }
607 }
608
609 void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
610 assert(ShenandoahPacing, "should only call when pacing is enabled");
611 Atomic::add(&_allocs_seen, words, memory_order_relaxed);
612 }
613
614 void ShenandoahControlThread::set_forced_counters_update(bool value) {
615 _force_counters_update.set_cond(value);
616 }
617
618 void ShenandoahControlThread::reset_gc_id() {
619 Atomic::store(&_gc_id, (size_t)0);
620 }
621
622 void ShenandoahControlThread::update_gc_id() {
623 Atomic::inc(&_gc_id);
624 }
625
626 size_t ShenandoahControlThread::get_gc_id() {
627 return Atomic::load(&_gc_id);
628 }
629
630 void ShenandoahControlThread::start() {
631 create_and_start();
632 }
633
634 void ShenandoahControlThread::prepare_for_graceful_shutdown() {
635 _graceful_shutdown.set();
636 }
637
638 bool ShenandoahControlThread::in_graceful_shutdown() {
639 return _graceful_shutdown.is_set();
640 }
|
1 /*
2 * Copyright (c) 2013, 2021, Red Hat, Inc. All rights reserved.
3 * Copyright (C) 2022 THL A29 Limited, a Tencent company. All rights reserved.
4 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
5 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
6 *
7 * This code is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License version 2 only, as
9 * published by the Free Software Foundation.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 *
25 */
26
27 #include "precompiled.hpp"
28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
29 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
30 #include "gc/shenandoah/shenandoahControlThread.hpp"
31 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
32 #include "gc/shenandoah/shenandoahEvacTracker.hpp"
33 #include "gc/shenandoah/shenandoahFreeSet.hpp"
34 #include "gc/shenandoah/shenandoahFullGC.hpp"
35 #include "gc/shenandoah/shenandoahGeneration.hpp"
36 #include "gc/shenandoah/shenandoahGlobalGeneration.hpp"
37 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
38 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
39 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
40 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
41 #include "gc/shenandoah/shenandoahMark.inline.hpp"
42 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
43 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
44 #include "gc/shenandoah/shenandoahOldGC.hpp"
45 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
46 #include "gc/shenandoah/shenandoahUtils.hpp"
47 #include "gc/shenandoah/shenandoahVMOperations.hpp"
48 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
49 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
50 #include "gc/shenandoah/mode/shenandoahMode.hpp"
51 #include "memory/iterator.hpp"
52 #include "memory/metaspaceUtils.hpp"
53 #include "memory/metaspaceStats.hpp"
54 #include "memory/universe.hpp"
55 #include "runtime/atomic.hpp"
56
57 ShenandoahControlThread::ShenandoahControlThread() :
58 ConcurrentGCThread(),
59 _alloc_failure_waiters_lock(Mutex::safepoint - 2, "ShenandoahAllocFailureGC_lock", true),
60 _gc_waiters_lock(Mutex::safepoint - 2, "ShenandoahRequestedGC_lock", true),
61 _control_lock(Mutex::nosafepoint - 2, "ShenandoahControlGC_lock", true),
62 _regulator_lock(Mutex::nosafepoint - 2, "ShenandoahRegulatorGC_lock", true),
63 _periodic_task(this),
64 _requested_gc_cause(GCCause::_no_cause_specified),
65 _requested_generation(select_global_generation()),
66 _degen_point(ShenandoahGC::_degenerated_outside_cycle),
67 _degen_generation(nullptr),
68 _allocs_seen(0),
69 _mode(none) {
70 set_name("Shenandoah Control Thread");
71 reset_gc_id();
72 create_and_start();
73 _periodic_task.enroll();
74 if (ShenandoahPacing) {
75 _periodic_pacer_notify_task.enroll();
76 }
77 }
78
79 ShenandoahControlThread::~ShenandoahControlThread() {
80 // This is here so that super is called.
81 }
82
83 void ShenandoahPeriodicTask::task() {
84 _thread->handle_force_counters_update();
85 _thread->handle_counters_update();
86 }
87
88 void ShenandoahPeriodicPacerNotify::task() {
89 assert(ShenandoahPacing, "Should not be here otherwise");
90 ShenandoahHeap::heap()->pacer()->notify_waiters();
91 }
92
93 void ShenandoahControlThread::run_service() {
94 ShenandoahHeap* heap = ShenandoahHeap::heap();
95
96 GCMode default_mode = concurrent_normal;
97 ShenandoahGenerationType generation = select_global_generation();
98 GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
99
100 double last_shrink_time = os::elapsedTime();
101 uint age_period = 0;
102
103 // Shrink period avoids constantly polling regions for shrinking.
104 // Having a period 10x lower than the delay would mean we hit the
105 // shrinking with lag of less than 1/10-th of true delay.
106 // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
107 double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
108
109 ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
110
111 // Heuristics are notified of allocation failures here and other outcomes
112 // of the cycle. They're also used here to control whether the Nth consecutive
113 // degenerated cycle should be 'promoted' to a full cycle. The decision to
114 // trigger a cycle or not is evaluated on the regulator thread.
115 ShenandoahHeuristics* global_heuristics = heap->global_generation()->heuristics();
116 bool old_bootstrap_requested = false;
117 while (!in_graceful_shutdown() && !should_terminate()) {
118 // Figure out if we have pending requests.
119 bool alloc_failure_pending = _alloc_failure_gc.is_set();
120 bool is_gc_requested = _gc_requested.is_set();
121 GCCause::Cause requested_gc_cause = _requested_gc_cause;
122 bool explicit_gc_requested = is_gc_requested && is_explicit_gc(requested_gc_cause);
123 bool implicit_gc_requested = is_gc_requested && is_implicit_gc(requested_gc_cause);
124
125 // This control loop iteration have seen this much allocations.
126 size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0, memory_order_relaxed);
127
128 // Check if we have seen a new target for soft max heap size.
129 bool soft_max_changed = check_soft_max_changed();
130
131 // Choose which GC mode to run in. The block below should select a single mode.
132 set_gc_mode(none);
133 GCCause::Cause cause = GCCause::_last_gc_cause;
134 ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
135
136 if (alloc_failure_pending) {
137 // Allocation failure takes precedence: we have to deal with it first thing
138 log_info(gc)("Trigger: Handle Allocation Failure");
139
140 cause = GCCause::_allocation_failure;
141
142 // Consume the degen point, and seed it with default value
143 degen_point = _degen_point;
144 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
145
146 if (degen_point == ShenandoahGC::_degenerated_outside_cycle) {
147 _degen_generation = heap->mode()->is_generational() ?
148 heap->young_generation() : heap->global_generation();
149 } else {
150 assert(_degen_generation != nullptr, "Need to know which generation to resume");
151 }
152
153 ShenandoahHeuristics* heuristics = _degen_generation->heuristics();
154 generation = _degen_generation->type();
155 bool old_gen_evacuation_failed = heap->clear_old_evacuation_failure();
156
157 // Do not bother with degenerated cycle if old generation evacuation failed
158 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle() && !old_gen_evacuation_failed) {
159 heuristics->record_allocation_failure_gc();
160 policy->record_alloc_failure_to_degenerated(degen_point);
161 set_gc_mode(stw_degenerated);
162 } else {
163 heuristics->record_allocation_failure_gc();
164 policy->record_alloc_failure_to_full();
165 generation = select_global_generation();
166 set_gc_mode(stw_full);
167 }
168 } else if (explicit_gc_requested) {
169 cause = requested_gc_cause;
170 generation = select_global_generation();
171 log_info(gc)("Trigger: Explicit GC request (%s)", GCCause::to_string(cause));
172
173 global_heuristics->record_requested_gc();
174
175 if (ExplicitGCInvokesConcurrent) {
176 policy->record_explicit_to_concurrent();
177 set_gc_mode(default_mode);
178 // Unload and clean up everything
179 heap->set_unload_classes(global_heuristics->can_unload_classes());
180 } else {
181 policy->record_explicit_to_full();
182 set_gc_mode(stw_full);
183 }
184 } else if (implicit_gc_requested) {
185 cause = requested_gc_cause;
186 generation = select_global_generation();
187 log_info(gc)("Trigger: Implicit GC request (%s)", GCCause::to_string(cause));
188
189 global_heuristics->record_requested_gc();
190
191 if (ShenandoahImplicitGCInvokesConcurrent) {
192 policy->record_implicit_to_concurrent();
193 set_gc_mode(default_mode);
194
195 // Unload and clean up everything
196 heap->set_unload_classes(global_heuristics->can_unload_classes());
197 } else {
198 policy->record_implicit_to_full();
199 set_gc_mode(stw_full);
200 }
201 } else {
202 // We should only be here if the regulator requested a cycle or if
203 // there is an old generation mark in progress.
204 if (_requested_gc_cause == GCCause::_shenandoah_concurrent_gc) {
205 if (_requested_generation == OLD && heap->doing_mixed_evacuations()) {
206 // If a request to start an old cycle arrived while an old cycle was running, but _before_
207 // it chose any regions for evacuation we don't want to start a new old cycle. Rather, we want
208 // the heuristic to run a young collection so that we can evacuate some old regions.
209 assert(!heap->is_concurrent_old_mark_in_progress(), "Should not be running mixed collections and concurrent marking");
210 generation = YOUNG;
211 } else if (_requested_generation == OLD && !old_bootstrap_requested) {
212 // Arrange to perform a young GC immediately followed by a bootstrap OLD GC. OLD GC typically requires more
213 // than twice the time required for YOUNG GC, so we run a YOUNG GC to replenish the YOUNG allocation pool before
214 // we start the longer OLD GC effort.
215 old_bootstrap_requested = true;
216 generation = YOUNG;
217 } else {
218 // if (old_bootstrap_requested && (_requested_generation == OLD)), this starts the bootstrap GC that
219 // immediately follows the preparatory young GC.
220 // But we will abandon the planned bootstrap GC if a GLOBAL GC has been now been requested.
221 generation = _requested_generation;
222 old_bootstrap_requested = false;
223 }
224 // preemption was requested or this is a regular cycle
225 cause = GCCause::_shenandoah_concurrent_gc;
226 set_gc_mode(default_mode);
227
228 // Don't start a new old marking if there is one already in progress
229 if (generation == OLD && heap->is_concurrent_old_mark_in_progress()) {
230 set_gc_mode(servicing_old);
231 }
232
233 if (generation == select_global_generation()) {
234 heap->set_unload_classes(global_heuristics->should_unload_classes());
235 } else {
236 heap->set_unload_classes(false);
237 }
238
239 // Don't want to spin in this loop and start a cycle every time, so
240 // clear requested gc cause. This creates a race with callers of the
241 // blocking 'request_gc' method, but there it loops and resets the
242 // '_requested_gc_cause' until a full cycle is completed.
243 _requested_gc_cause = GCCause::_no_gc;
244 } else if (heap->is_concurrent_old_mark_in_progress() || heap->is_prepare_for_old_mark_in_progress()) {
245 // Nobody asked us to do anything, but we have an old-generation mark or old-generation preparation for
246 // mixed evacuation in progress, so resume working on that.
247 log_info(gc)("Resume old GC: marking is%s in progress, preparing is%s in progress",
248 heap->is_concurrent_old_mark_in_progress() ? "" : " NOT",
249 heap->is_prepare_for_old_mark_in_progress() ? "" : " NOT");
250
251 cause = GCCause::_shenandoah_concurrent_gc;
252 generation = OLD;
253 set_gc_mode(servicing_old);
254 }
255 }
256
257 // Blow all soft references on this cycle, if handling allocation failure,
258 // either implicit or explicit GC request, or we are requested to do so unconditionally.
259 if (generation == select_global_generation() && (alloc_failure_pending || implicit_gc_requested || explicit_gc_requested || ShenandoahAlwaysClearSoftRefs)) {
260 heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
261 }
262
263 bool gc_requested = (_mode != none);
264 assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
265
266 if (gc_requested) {
267 // GC is starting, bump the internal ID
268 update_gc_id();
269
270 heap->reset_bytes_allocated_since_gc_start();
271
272 MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
273
274 // If GC was requested, we are sampling the counters even without actual triggers
275 // from allocation machinery. This captures GC phases more accurately.
276 set_forced_counters_update(true);
277
278 // If GC was requested, we better dump freeset data for performance debugging
279 {
280 ShenandoahHeapLocker locker(heap->lock());
281 heap->free_set()->log_status();
282 }
283 // In case this is a degenerated cycle, remember whether original cycle was aging.
284 bool was_aging_cycle = heap->is_aging_cycle();
285 heap->set_aging_cycle(false);
286
287 switch (_mode) {
288 case concurrent_normal: {
289 // At this point:
290 // if (generation == YOUNG), this is a normal YOUNG cycle
291 // if (generation == OLD), this is a bootstrap OLD cycle
292 // if (generation == GLOBAL), this is a GLOBAL cycle triggered by System.gc()
293 // In all three cases, we want to age old objects if this is an aging cycle
294 if (age_period-- == 0) {
295 heap->set_aging_cycle(true);
296 age_period = ShenandoahAgingCyclePeriod - 1;
297 }
298 service_concurrent_normal_cycle(heap, generation, cause);
299 break;
300 }
301 case stw_degenerated: {
302 heap->set_aging_cycle(was_aging_cycle);
303 if (!service_stw_degenerated_cycle(cause, degen_point)) {
304 // The degenerated GC was upgraded to a Full GC
305 generation = select_global_generation();
306 }
307 break;
308 }
309 case stw_full: {
310 if (age_period-- == 0) {
311 heap->set_aging_cycle(true);
312 age_period = ShenandoahAgingCyclePeriod - 1;
313 }
314 service_stw_full_cycle(cause);
315 break;
316 }
317 case servicing_old: {
318 assert(generation == OLD, "Expected old generation here");
319 GCIdMark gc_id_mark;
320 service_concurrent_old_cycle(heap, cause);
321 break;
322 }
323 default:
324 ShouldNotReachHere();
325 }
326
327 // If this was the requested GC cycle, notify waiters about it
328 if (explicit_gc_requested || implicit_gc_requested) {
329 notify_gc_waiters();
330 }
331
332 // If this was the allocation failure GC cycle, notify waiters about it
333 if (alloc_failure_pending) {
334 notify_alloc_failure_waiters();
335 }
336
337 // Report current free set state at the end of cycle, whether
338 // it is a normal completion, or the abort.
339 {
340 ShenandoahHeapLocker locker(heap->lock());
341 heap->free_set()->log_status();
342
343 // Notify Universe about new heap usage. This has implications for
344 // global soft refs policy, and we better report it every time heap
345 // usage goes down.
346 Universe::heap()->update_capacity_and_used_at_gc();
347
348 // Signal that we have completed a visit to all live objects.
349 Universe::heap()->record_whole_heap_examined_timestamp();
350 }
351
352 // Disable forced counters update, and update counters one more time
353 // to capture the state at the end of GC session.
354 handle_force_counters_update();
355 set_forced_counters_update(false);
356
357 // Retract forceful part of soft refs policy
358 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
359
360 // Clear metaspace oom flag, if current cycle unloaded classes
361 if (heap->unload_classes()) {
362 assert(generation == select_global_generation(), "Only unload classes during GLOBAL cycle");
363 global_heuristics->clear_metaspace_oom();
364 }
365
366 process_phase_timings(heap);
367
368 // Print Metaspace change following GC (if logging is enabled).
369 MetaspaceUtils::print_metaspace_change(meta_sizes);
370
371 // GC is over, we are at idle now
372 if (ShenandoahPacing) {
373 heap->pacer()->setup_for_idle();
374 }
375 } else {
376 // Allow allocators to know we have seen this much regions
377 if (ShenandoahPacing && (allocs_seen > 0)) {
378 heap->pacer()->report_alloc(allocs_seen);
379 }
380 }
381
382 double current = os::elapsedTime();
383
384 if (ShenandoahUncommit && (explicit_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
385 // Explicit GC tries to uncommit everything down to min capacity.
386 // Soft max change tries to uncommit everything down to target capacity.
387 // Periodic uncommit tries to uncommit suitable regions down to min capacity.
388
389 double shrink_before = (explicit_gc_requested || soft_max_changed) ?
390 current :
391 current - (ShenandoahUncommitDelay / 1000.0);
392
393 size_t shrink_until = soft_max_changed ?
394 heap->soft_max_capacity() :
395 heap->min_capacity();
396
397 service_uncommit(shrink_before, shrink_until);
398 heap->phase_timings()->flush_cycle_to_global();
399 last_shrink_time = current;
400 }
401
402 // Don't wait around if there was an allocation failure - start the next cycle immediately.
403 if (!is_alloc_failure_gc()) {
404 if (old_bootstrap_requested) {
405 _requested_generation = OLD;
406 _requested_gc_cause = GCCause::_shenandoah_concurrent_gc;
407 } else {
408 // The timed wait is necessary because this thread has a responsibility to send
409 // 'alloc_words' to the pacer when it does not perform a GC.
410 MonitorLocker lock(&_control_lock, Mutex::_no_safepoint_check_flag);
411 lock.wait(ShenandoahControlIntervalMax);
412 }
413 } else {
414 // in case of alloc_failure, abandon any plans to do immediate OLD Bootstrap
415 old_bootstrap_requested = false;
416 }
417 }
418
419 // Wait for the actual stop(), can't leave run_service() earlier.
420 while (!should_terminate()) {
421 os::naked_short_sleep(ShenandoahControlIntervalMin);
422 }
423 }
424
425 void ShenandoahControlThread::process_phase_timings(const ShenandoahHeap* heap) {
426 // Commit worker statistics to cycle data
427 heap->phase_timings()->flush_par_workers_to_cycle();
428 if (ShenandoahPacing) {
429 heap->pacer()->flush_stats_to_cycle();
430 }
431
432 ShenandoahCycleStats evac_stats = heap->evac_tracker()->flush_cycle_to_global();
433
434 // Print GC stats for current cycle
435 {
436 LogTarget(Info, gc, stats) lt;
437 if (lt.is_enabled()) {
438 ResourceMark rm;
439 LogStream ls(lt);
440 heap->phase_timings()->print_cycle_on(&ls);
441 ShenandoahEvacuationTracker::print_evacuations_on(&ls, &evac_stats.workers,
442 &evac_stats.mutators);
443 if (ShenandoahPacing) {
444 heap->pacer()->print_cycle_on(&ls);
445 }
446 }
447 }
448
449 // Commit statistics to globals
450 heap->phase_timings()->flush_cycle_to_global();
451 }
452
453 // Young and old concurrent cycles are initiated by the regulator. Implicit
454 // and explicit GC requests are handled by the controller thread and always
455 // run a global cycle (which is concurrent by default, but may be overridden
456 // by command line options). Old cycles always degenerate to a global cycle.
457 // Young cycles are degenerated to complete the young cycle. Young
458 // and old degen may upgrade to Full GC. Full GC may also be
459 // triggered directly by a System.gc() invocation.
460 //
461 //
462 // +-----+ Idle +-----+-----------+---------------------+
463 // | + | | |
464 // | | | | |
465 // | | v | |
466 // | | Bootstrap Old +-- | ------------+ |
467 // | | + | | |
468 // | | | | | |
469 // | v v v v |
470 // | Resume Old <----------+ Young +--> Young Degen |
471 // | + + ^ + + |
472 // v | | | | | |
473 // Global <-+ | +----------------------------+ | |
474 // + | | |
475 // | v v |
476 // +---> Global Degen +--------------------> Full <----+
477 //
478 void ShenandoahControlThread::service_concurrent_normal_cycle(ShenandoahHeap* heap,
479 const ShenandoahGenerationType generation,
480 GCCause::Cause cause) {
481 GCIdMark gc_id_mark;
482 ShenandoahGeneration* the_generation = nullptr;
483 switch (generation) {
484 case YOUNG: {
485 // Run a young cycle. This might or might not, have interrupted an ongoing
486 // concurrent mark in the old generation. We need to think about promotions
487 // in this case. Promoted objects should be above the TAMS in the old regions
488 // they end up in, but we have to be sure we don't promote into any regions
489 // that are in the cset.
490 log_info(gc, ergo)("Start GC cycle (YOUNG)");
491 the_generation = heap->young_generation();
492 service_concurrent_cycle(the_generation, cause, false);
493 break;
494 }
495 case OLD: {
496 log_info(gc, ergo)("Start GC cycle (OLD)");
497 the_generation = heap->old_generation();
498 service_concurrent_old_cycle(heap, cause);
499 break;
500 }
501 case GLOBAL_GEN: {
502 log_info(gc, ergo)("Start GC cycle (GLOBAL)");
503 the_generation = heap->global_generation();
504 service_concurrent_cycle(the_generation, cause, false);
505 break;
506 }
507 case GLOBAL_NON_GEN: {
508 log_info(gc, ergo)("Start GC cycle");
509 the_generation = heap->global_generation();
510 service_concurrent_cycle(the_generation, cause, false);
511 break;
512 }
513 default:
514 ShouldNotReachHere();
515 }
516 }
517
518 void ShenandoahControlThread::service_concurrent_old_cycle(ShenandoahHeap* heap, GCCause::Cause &cause) {
519 ShenandoahOldGeneration* old_generation = heap->old_generation();
520 ShenandoahYoungGeneration* young_generation = heap->young_generation();
521 ShenandoahOldGeneration::State original_state = old_generation->state();
522
523 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
524
525 switch (original_state) {
526 case ShenandoahOldGeneration::WAITING_FOR_FILL:
527 case ShenandoahOldGeneration::IDLE: {
528 assert(!heap->is_concurrent_old_mark_in_progress(), "Old already in progress");
529 assert(old_generation->task_queues()->is_empty(), "Old mark queues should be empty");
530 }
531 case ShenandoahOldGeneration::FILLING: {
532 _allow_old_preemption.set();
533 ShenandoahGCSession session(cause, old_generation);
534 old_generation->prepare_gc();
535 _allow_old_preemption.unset();
536
537 if (heap->is_prepare_for_old_mark_in_progress()) {
538 // Coalescing threads detected the cancellation request and aborted. Stay
539 // in this state so control thread may resume the coalescing work.
540 assert(old_generation->state() == ShenandoahOldGeneration::FILLING, "Prepare for mark should be in progress");
541 return;
542 }
543
544 // It is possible for a young generation request to preempt this nascent old
545 // collection cycle _after_ we've finished making the old regions parseable (filling),
546 // but _before_ we have unset the preemption flag. It is also possible for an
547 // allocation failure to occur after the threads have finished filling. We must
548 // check if we have been cancelled before we start a bootstrap cycle.
549 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) {
550 if (heap->cancelled_gc()) {
551 // If this was a preemption request, the cancellation would have been cleared
552 // so that we run a concurrent young cycle. If the cancellation is still set,
553 // then this is an allocation failure and we need to run a degenerated cycle.
554 // If this is a preemption request, we're just going to fall through and run
555 // the bootstrap cycle to start the old generation cycle (the bootstrap cycle is
556 // a concurrent young cycle - which is what we're being asked to do in that case).
557 // If the cycle is cancelled for any other reason, we return from here and let
558 // the control thread return to the top of its decision loop.
559 log_info(gc)("Preparation for old generation cycle was cancelled");
560 return;
561 }
562 }
563 old_generation->transition_to(ShenandoahOldGeneration::BOOTSTRAPPING);
564 }
565 case ShenandoahOldGeneration::BOOTSTRAPPING: {
566 // Configure the young generation's concurrent mark to put objects in
567 // old regions into the concurrent mark queues associated with the old
568 // generation. The young cycle will run as normal except that rather than
569 // ignore old references it will mark and enqueue them in the old concurrent
570 // task queues but it will not traverse them.
571 set_gc_mode(bootstrapping_old);
572 young_generation->set_old_gen_task_queues(old_generation->task_queues());
573 ShenandoahGCSession session(cause, young_generation);
574 service_concurrent_cycle(heap, young_generation, cause, true);
575 process_phase_timings(heap);
576 if (heap->cancelled_gc()) {
577 // Young generation bootstrap cycle has failed. Concurrent mark for old generation
578 // is going to resume after degenerated bootstrap cycle completes.
579 log_info(gc)("Bootstrap cycle for old generation was cancelled");
580 return;
581 }
582
583 // Reset the degenerated point. Normally this would happen at the top
584 // of the control loop, but here we have just completed a young cycle
585 // which has bootstrapped the old concurrent marking.
586 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
587
588 // From here we will 'resume' the old concurrent mark. This will skip reset
589 // and init mark for the concurrent mark. All of that work will have been
590 // done by the bootstrapping young cycle.
591 set_gc_mode(servicing_old);
592 old_generation->transition_to(ShenandoahOldGeneration::MARKING);
593 }
594 case ShenandoahOldGeneration::MARKING: {
595 ShenandoahGCSession session(cause, old_generation);
596 bool marking_complete = resume_concurrent_old_cycle(old_generation, cause);
597 if (marking_complete) {
598 assert(old_generation->state() != ShenandoahOldGeneration::MARKING, "Should not still be marking");
599 if (original_state == ShenandoahOldGeneration::MARKING) {
600 heap->mmu_tracker()->record_old_marking_increment(old_generation, GCId::current(), true,
601 heap->collection_set()->has_old_regions());
602 heap->log_heap_status("At end of Concurrent Old Marking finishing increment");
603 }
604 } else if (original_state == ShenandoahOldGeneration::MARKING) {
605 heap->mmu_tracker()->record_old_marking_increment(old_generation, GCId::current(), false,
606 heap->collection_set()->has_old_regions());
607 heap->log_heap_status("At end of Concurrent Old Marking increment");
608 }
609 break;
610 }
611 default:
612 fatal("Unexpected state for old GC: %s", ShenandoahOldGeneration::state_name(old_generation->state()));
613 }
614 }
615
616 bool ShenandoahControlThread::resume_concurrent_old_cycle(ShenandoahGeneration* generation, GCCause::Cause cause) {
617 assert(ShenandoahHeap::heap()->is_concurrent_old_mark_in_progress(), "Old mark should be in progress");
618 log_debug(gc)("Resuming old generation with " UINT32_FORMAT " marking tasks queued", generation->task_queues()->tasks());
619
620 ShenandoahHeap* heap = ShenandoahHeap::heap();
621
622 // We can only tolerate being cancelled during concurrent marking or during preparation for mixed
623 // evacuation. This flag here (passed by reference) is used to control precisely where the regulator
624 // is allowed to cancel a GC.
625 ShenandoahOldGC gc(generation, _allow_old_preemption);
626 if (gc.collect(cause)) {
627 generation->record_success_concurrent(false);
628 }
629
630 if (heap->cancelled_gc()) {
631 // It's possible the gc cycle was cancelled after the last time
632 // the collection checked for cancellation. In which case, the
633 // old gc cycle is still completed, and we have to deal with this
634 // cancellation. We set the degeneration point to be outside
635 // the cycle because if this is an allocation failure, that is
636 // what must be done (there is no degenerated old cycle). If the
637 // cancellation was due to a heuristic wanting to start a young
638 // cycle, then we are not actually going to a degenerated cycle,
639 // so the degenerated point doesn't matter here.
640 check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle);
641 if (_requested_gc_cause == GCCause::_shenandoah_concurrent_gc) {
642 heap->shenandoah_policy()->record_interrupted_old();
643 }
644 return false;
645 }
646 return true;
647 }
648
649 bool ShenandoahControlThread::check_soft_max_changed() const {
650 ShenandoahHeap* heap = ShenandoahHeap::heap();
651 size_t new_soft_max = Atomic::load(&SoftMaxHeapSize);
652 size_t old_soft_max = heap->soft_max_capacity();
653 if (new_soft_max != old_soft_max) {
654 new_soft_max = MAX2(heap->min_capacity(), new_soft_max);
655 new_soft_max = MIN2(heap->max_capacity(), new_soft_max);
656 if (new_soft_max != old_soft_max) {
657 log_info(gc)("Soft Max Heap Size: " SIZE_FORMAT "%s -> " SIZE_FORMAT "%s",
658 byte_size_in_proper_unit(old_soft_max), proper_unit_for_byte_size(old_soft_max),
659 byte_size_in_proper_unit(new_soft_max), proper_unit_for_byte_size(new_soft_max)
660 );
661 heap->set_soft_max_capacity(new_soft_max);
662 return true;
663 }
664 }
665 return false;
666 }
667
668 void ShenandoahControlThread::service_concurrent_cycle(ShenandoahGeneration* generation, GCCause::Cause cause, bool do_old_gc_bootstrap) {
669 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
670 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
671 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
672 // tries to evac something and no memory is available), cycle degrades to Full GC.
673 //
674 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
675 // heuristics says there are no regions to compact, and all the collection comes from immediately
676 // reclaimable regions.
677 //
678 // ................................................................................................
679 //
680 // (immediate garbage shortcut) Concurrent GC
681 // /-------------------------------------------\
682 // | |
683 // | |
684 // | |
685 // | v
686 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
687 // | | | ^
688 // | (af) | (af) | (af) |
689 // ..................|....................|.................|..............|.......................
690 // | | | |
691 // | | | | Degenerated GC
692 // v v v |
693 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
694 // | | | ^
695 // | (af) | (af) | (af) |
696 // ..................|....................|.................|..............|.......................
697 // | | | |
698 // | v | | Full GC
699 // \------------------->o<----------------/ |
700 // | |
701 // v |
702 // Full GC --------------------------/
703 //
704 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
705
706 ShenandoahHeap* heap = ShenandoahHeap::heap();
707 ShenandoahGCSession session(cause, generation);
708 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
709
710 service_concurrent_cycle(heap, generation, cause, do_old_gc_bootstrap);
711 }
712
713 void ShenandoahControlThread::service_concurrent_cycle(ShenandoahHeap* heap,
714 ShenandoahGeneration* generation,
715 GCCause::Cause& cause,
716 bool do_old_gc_bootstrap) {
717 ShenandoahConcurrentGC gc(generation, do_old_gc_bootstrap);
718 if (gc.collect(cause)) {
719 // Cycle is complete
720 generation->record_success_concurrent(gc.abbreviated());
721 } else {
722 assert(heap->cancelled_gc(), "Must have been cancelled");
723 check_cancellation_or_degen(gc.degen_point());
724 assert(!generation->is_old(), "Old GC takes a different control path");
725 // Concurrent young-gen collection degenerates to young
726 // collection. Same for global collections.
727 _degen_generation = generation;
728 }
729 const char* msg;
730 if (heap->mode()->is_generational()) {
731 if (heap->cancelled_gc()) {
732 msg = (generation->is_young()) ? "At end of Interrupted Concurrent Young GC" :
733 "At end of Interrupted Concurrent Bootstrap GC";
734 } else {
735 msg = (generation->is_young()) ? "At end of Concurrent Young GC" :
736 "At end of Concurrent Bootstrap GC";
737 // We only record GC results if GC was successful
738 ShenandoahMmuTracker* mmu_tracker = heap->mmu_tracker();
739 if (generation->is_young()) {
740 if (heap->collection_set()->has_old_regions()) {
741 bool mixed_is_done = (heap->old_heuristics()->unprocessed_old_collection_candidates() == 0);
742 mmu_tracker->record_mixed(generation, get_gc_id(), mixed_is_done);
743 } else {
744 mmu_tracker->record_young(generation, get_gc_id());
745 }
746 } else {
747 mmu_tracker->record_bootstrap(generation, get_gc_id(), heap->collection_set()->has_old_regions());
748 }
749 }
750 } else {
751 msg = heap->cancelled_gc() ? "At end of cancelled GC" :
752 "At end of GC";
753 }
754 heap->log_heap_status(msg);
755 }
756
757 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
758 ShenandoahHeap* heap = ShenandoahHeap::heap();
759 if (!heap->cancelled_gc()) {
760 return false;
761 }
762
763 if (in_graceful_shutdown()) {
764 return true;
765 }
766
767 assert(_degen_point == ShenandoahGC::_degenerated_outside_cycle,
768 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
769
770 if (is_alloc_failure_gc()) {
771 _degen_point = point;
772 return true;
773 }
774
775 if (_preemption_requested.is_set()) {
776 assert(_requested_generation == YOUNG, "Only young GCs may preempt old.");
777 _preemption_requested.unset();
778
779 // Old generation marking is only cancellable during concurrent marking.
780 // Once final mark is complete, the code does not check again for cancellation.
781 // If old generation was cancelled for an allocation failure, we wouldn't
782 // make it to this case. The calling code is responsible for forcing a
783 // cancellation due to allocation failure into a degenerated cycle.
784 _degen_point = point;
785 heap->clear_cancelled_gc(false /* clear oom handler */);
786 return true;
787 }
788
789 fatal("Cancel GC either for alloc failure GC, or gracefully exiting, or to pause old generation marking");
790 return false;
791 }
792
793 void ShenandoahControlThread::stop_service() {
794 // Nothing to do here.
795 }
796
797 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
798 ShenandoahHeap* const heap = ShenandoahHeap::heap();
799
800 GCIdMark gc_id_mark;
801 ShenandoahGCSession session(cause, heap->global_generation());
802
803 ShenandoahFullGC gc;
804 gc.collect(cause);
805
806 heap->global_generation()->heuristics()->record_success_full();
807 heap->shenandoah_policy()->record_success_full();
808 }
809
810 bool ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause,
811 ShenandoahGC::ShenandoahDegenPoint point) {
812 assert(point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
813 ShenandoahHeap* const heap = ShenandoahHeap::heap();
814
815 GCIdMark gc_id_mark;
816 ShenandoahGCSession session(cause, _degen_generation);
817
818 ShenandoahDegenGC gc(point, _degen_generation);
819 gc.collect(cause);
820
821 assert(heap->young_generation()->task_queues()->is_empty(), "Unexpected young generation marking tasks");
822 if (_degen_generation->is_global()) {
823 assert(heap->old_generation()->task_queues()->is_empty(), "Unexpected old generation marking tasks");
824 assert(heap->global_generation()->task_queues()->is_empty(), "Unexpected global generation marking tasks");
825 } else {
826 assert(_degen_generation->is_young(), "Expected degenerated young cycle, if not global.");
827 ShenandoahOldGeneration* old = heap->old_generation();
828 if (old->state() == ShenandoahOldGeneration::BOOTSTRAPPING && !gc.upgraded_to_full()) {
829 old->transition_to(ShenandoahOldGeneration::MARKING);
830 }
831 }
832
833 _degen_generation->heuristics()->record_success_degenerated();
834 heap->shenandoah_policy()->record_success_degenerated();
835 return !gc.upgraded_to_full();
836 }
837
838 void ShenandoahControlThread::service_uncommit(double shrink_before, size_t shrink_until) {
839 ShenandoahHeap* heap = ShenandoahHeap::heap();
840
841 // Determine if there is work to do. This avoids taking heap lock if there is
842 // no work available, avoids spamming logs with superfluous logging messages,
843 // and minimises the amount of work while locks are taken.
844
845 if (heap->committed() <= shrink_until) return;
846
847 bool has_work = false;
848 for (size_t i = 0; i < heap->num_regions(); i++) {
849 ShenandoahHeapRegion *r = heap->get_region(i);
850 if (r->is_empty_committed() && (r->empty_time() < shrink_before)) {
851 has_work = true;
852 break;
853 }
854 }
855
856 if (has_work) {
857 heap->entry_uncommit(shrink_before, shrink_until);
858 }
859 }
860
861 bool ShenandoahControlThread::is_explicit_gc(GCCause::Cause cause) const {
862 return GCCause::is_user_requested_gc(cause) ||
863 GCCause::is_serviceability_requested_gc(cause);
864 }
865
866 bool ShenandoahControlThread::is_implicit_gc(GCCause::Cause cause) const {
867 return !is_explicit_gc(cause) &&
868 (cause != GCCause::_shenandoah_concurrent_gc);
869 }
870
871 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
872 assert(GCCause::is_user_requested_gc(cause) ||
873 GCCause::is_serviceability_requested_gc(cause) ||
874 cause == GCCause::_metadata_GC_clear_soft_refs ||
875 cause == GCCause::_codecache_GC_aggressive ||
876 cause == GCCause::_codecache_GC_threshold ||
877 cause == GCCause::_full_gc_alot ||
878 cause == GCCause::_wb_young_gc ||
879 cause == GCCause::_wb_full_gc ||
880 cause == GCCause::_wb_breakpoint ||
881 cause == GCCause::_scavenge_alot,
882 "only requested GCs here: %s", GCCause::to_string(cause));
883
884 if (is_explicit_gc(cause)) {
885 if (!DisableExplicitGC) {
886 handle_requested_gc(cause);
887 }
888 } else {
889 handle_requested_gc(cause);
890 }
891 }
892
893 bool ShenandoahControlThread::request_concurrent_gc(ShenandoahGenerationType generation) {
894 if (_preemption_requested.is_set() || _gc_requested.is_set() || ShenandoahHeap::heap()->cancelled_gc()) {
895 // Ignore subsequent requests from the heuristics
896 return false;
897 }
898
899 if (_mode == none) {
900 _requested_gc_cause = GCCause::_shenandoah_concurrent_gc;
901 _requested_generation = generation;
902 notify_control_thread();
903 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
904 ml.wait();
905 return true;
906 }
907
908 if (preempt_old_marking(generation)) {
909 log_info(gc)("Preempting old generation mark to allow %s GC", shenandoah_generation_name(generation));
910 _requested_gc_cause = GCCause::_shenandoah_concurrent_gc;
911 _requested_generation = generation;
912 _preemption_requested.set();
913 ShenandoahHeap::heap()->cancel_gc(GCCause::_shenandoah_concurrent_gc);
914 notify_control_thread();
915
916 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
917 ml.wait();
918 return true;
919 }
920
921 return false;
922 }
923
924 void ShenandoahControlThread::notify_control_thread() {
925 MonitorLocker locker(&_control_lock, Mutex::_no_safepoint_check_flag);
926 _control_lock.notify();
927 }
928
929 bool ShenandoahControlThread::preempt_old_marking(ShenandoahGenerationType generation) {
930 return (generation == YOUNG) && _allow_old_preemption.try_unset();
931 }
932
933 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
934 // Make sure we have at least one complete GC cycle before unblocking
935 // from the explicit GC request.
936 //
937 // This is especially important for weak references cleanup and/or native
938 // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
939 // comes very late in the already running cycle, it would miss lots of new
940 // opportunities for cleanup that were made available before the caller
941 // requested the GC.
942
943 MonitorLocker ml(&_gc_waiters_lock);
944 size_t current_gc_id = get_gc_id();
945 size_t required_gc_id = current_gc_id + 1;
946 while (current_gc_id < required_gc_id) {
947 // Although setting gc request is under _gc_waiters_lock, but read side (run_service())
948 // does not take the lock. We need to enforce following order, so that read side sees
949 // latest requested gc cause when the flag is set.
950 _requested_gc_cause = cause;
951 _gc_requested.set();
952 notify_control_thread();
953 if (cause != GCCause::_wb_breakpoint) {
954 ml.wait();
955 }
956 current_gc_id = get_gc_id();
957 }
958 }
959
960 void ShenandoahControlThread::handle_alloc_failure(ShenandoahAllocRequest& req) {
961 ShenandoahHeap* heap = ShenandoahHeap::heap();
962
963 assert(current()->is_Java_thread(), "expect Java thread here");
964
965 if (try_set_alloc_failure_gc()) {
966 // Only report the first allocation failure
967 log_info(gc)("Failed to allocate %s, " SIZE_FORMAT "%s",
968 req.type_string(),
969 byte_size_in_proper_unit(req.size() * HeapWordSize), proper_unit_for_byte_size(req.size() * HeapWordSize));
970 // Now that alloc failure GC is scheduled, we can abort everything else
971 heap->cancel_gc(GCCause::_allocation_failure);
972 }
973
974 MonitorLocker ml(&_alloc_failure_waiters_lock);
975 while (is_alloc_failure_gc()) {
976 ml.wait();
977 }
978 }
979
980 void ShenandoahControlThread::handle_alloc_failure_evac(size_t words) {
981 ShenandoahHeap* heap = ShenandoahHeap::heap();
982
983 if (try_set_alloc_failure_gc()) {
984 // Only report the first allocation failure
985 log_info(gc)("Failed to allocate " SIZE_FORMAT "%s for evacuation",
986 byte_size_in_proper_unit(words * HeapWordSize), proper_unit_for_byte_size(words * HeapWordSize));
987 }
988
989 // Forcefully report allocation failure
1015 _do_counters_update.unset();
1016 ShenandoahHeap::heap()->monitoring_support()->update_counters();
1017 }
1018 }
1019
1020 void ShenandoahControlThread::handle_force_counters_update() {
1021 if (_force_counters_update.is_set()) {
1022 _do_counters_update.unset(); // reset these too, we do update now!
1023 ShenandoahHeap::heap()->monitoring_support()->update_counters();
1024 }
1025 }
1026
1027 void ShenandoahControlThread::notify_heap_changed() {
1028 // This is called from allocation path, and thus should be fast.
1029
1030 // Update monitoring counters when we took a new region. This amortizes the
1031 // update costs on slow path.
1032 if (_do_counters_update.is_unset()) {
1033 _do_counters_update.set();
1034 }
1035 }
1036
1037 void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
1038 assert(ShenandoahPacing, "should only call when pacing is enabled");
1039 Atomic::add(&_allocs_seen, words, memory_order_relaxed);
1040 }
1041
1042 void ShenandoahControlThread::set_forced_counters_update(bool value) {
1043 _force_counters_update.set_cond(value);
1044 }
1045
1046 void ShenandoahControlThread::reset_gc_id() {
1047 Atomic::store(&_gc_id, (size_t)0);
1048 }
1049
1050 void ShenandoahControlThread::update_gc_id() {
1051 Atomic::inc(&_gc_id);
1052 }
1053
1054 size_t ShenandoahControlThread::get_gc_id() {
1055 return Atomic::load(&_gc_id);
1056 }
1057
1058 void ShenandoahControlThread::start() {
1059 create_and_start();
1060 }
1061
1062 void ShenandoahControlThread::prepare_for_graceful_shutdown() {
1063 _graceful_shutdown.set();
1064 }
1065
1066 bool ShenandoahControlThread::in_graceful_shutdown() {
1067 return _graceful_shutdown.is_set();
1068 }
1069
1070 const char* ShenandoahControlThread::gc_mode_name(ShenandoahControlThread::GCMode mode) {
1071 switch (mode) {
1072 case none: return "idle";
1073 case concurrent_normal: return "normal";
1074 case stw_degenerated: return "degenerated";
1075 case stw_full: return "full";
1076 case servicing_old: return "old";
1077 case bootstrapping_old: return "bootstrap";
1078 default: return "unknown";
1079 }
1080 }
1081
1082 void ShenandoahControlThread::set_gc_mode(ShenandoahControlThread::GCMode new_mode) {
1083 if (_mode != new_mode) {
1084 log_info(gc)("Transition from: %s to: %s", gc_mode_name(_mode), gc_mode_name(new_mode));
1085 _mode = new_mode;
1086 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
1087 ml.notify_all();
1088 }
1089 }
1090
1091 ShenandoahGenerationType ShenandoahControlThread::select_global_generation() {
1092 if (ShenandoahHeap::heap()->mode()->is_generational()) {
1093 return GLOBAL_GEN;
1094 } else {
1095 return GLOBAL_NON_GEN;
1096 }
1097 }
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